Electric power source



Sept. l2, 1950 w. P. MAsoN ELECTRIF POWER SOURCE Filed March 16, 1946 ilfw. A V

l/VVE/VmR .By me MASON c. 21.4/ ATTGRNEY Patented Sept. 12, 1950ELECTRIC POWER SOURCE Warren P. Mason, West Orange, N. J., assigner toBell Telephone Laboratories, Incorporated, New York, N. Y., acorporation of New York Application March 16, 1946, Serial No. 655,001

17 Claims. l

'I'his invention relates to prime sources of energy and moreparticularly to a novel system for producing electrical energy in whichan electromechanical transducer is excited by mechanical vibrations ofan internal combustion device.

An object of the invention is to produce electrical energy by causingsuccessive explosions of a combustible vapor or .powdered fuel to inducevibrations in a vibratory electrical generator.

Another object of the invention is to convert the energy of burning fuelinto electrical energy with relatively little displacement of mechanicalmasses and without the use of rotating parts or elements of considerablemass.

Still another object of the invention is to utilize the energy of a highfrequency series of explosions to excite a piezo-electric element, amagnetostrictive element or other electro-mechanical transducer.

Another object is to provide a compression wave impedance transformerwhich shall be capable of transforming a very low source impedance tomatch a very high receiver impedance, or vice versa, without introducinglosses into the system.

In accordance with the invention a vessel or chamber, in whichexplosions of a suitable fuel take place in rapid sequence, is soproportioned as to support sustained gas pressure oscillations orstanding waves therein and the vibratory mechanical energy of theseoscillations is transferred, preferably by way of a novelimpedancematching device, to a mechanical-electrical transducer elementof appropriate type. This element, when actuated directly or indirectlyby the oscillatory mechanical energy of the explosions, developselectrical energy which may be withdrawn and utilized to supply adesired load.

It is a feature of the invention that the main chamber in which theexplosions take rplace is resonant or reverberant at the explosionfrequency or a harmonic multiple thereof, so that pressure oscillationsof large amplitude may be sustained with the addition of a comparativelysmall additional amount of explosive energy during each operating cycle.

It is another feature of the invention that the major portion of theoscillator pressure energy within the explosion chamber is transferred,directly or indirectly, to the mechanical-electrical transducer, meansbeing provided to prevent its escape with exhaust combustion products.

The invention in its various aspects will be more fully understood fromthe following detailed description of a preferred embodiment thereof,

2 taken in conjunction with the appended drawing, the single gure ofwhich shows a sectional diagram of the apparatus and a'schematicVdiagram of the associated electric circuit of an engine for convertingexplosive mechanical energy into electrical energy of like frequency.

Referring now to the gure, an explosion cham'- ber I is provided, closedat one end by a valve 2 and at the other by a light, stiff, movablepiston l. The chamber walls may be of any suitable strong,pressuresupporting material such as steel or cast iron. The chamber maybe surrounded by a water jacket 4 for cooling purposes. Fuel, forexample in the form of atomized liquid fuel, is supplied tothe chamberfrom a fuel tank 5 by way of a carburetor 6, an intake manifold 1 andthe intake valve 2, being forced in by a supercharger pump 8, driven bya motor 9. These elements may all be of conventional mechanical design..

The valve 2 is preferably operated electromagnetically as by a solenoidI0 to which energy is supplied from an electric circuit whose detailswill be described hereinafter. Ignition of the atomized fuel may beeffected by spark-gaps l I I,

likewise supplied from the electric circuit, in`

proper phase relation with the opening and closure of the intake valve2. Combustion products may be withdrawn by way of an exhaust pipe I2which is preferably provided with one or more filters I3 as more fullydescribed below.

At the' end of the explosion chamber I opposite to the head end in whichthe intake valve 2 and the spark-gaps II are mounted there is xedlymounted a light exible piston diaphragm Il, for example, of sheet metal,Whose peripheral skirt may be xed as by welding to the inside walls ofthe chamber I. The piston 3 may likewise be a light, flexible diaphragmwhose peripheral skirt is arranged to slide, over a short distance,within the skirt of the diaphragm I4. The separation between the pistondiaphragm I4 and the piston diaphragm 3, and therefore the position ofthe latter relative to the head end of the chamber I may be adjusted asby a turn buckle I5. These two diaphragms together form a partition ofadjustable length between the explosion chamber I and a second chamberI6, which is preferably of larger cross-section than the explosionchamber. This second chamber I6 is lled with a wave-supporting liquidsuch as water or oil. A partition, for example, a thin sheet I1 ofrubber or the like, divides this second chamber into two parts. Onepart, shown in the figureto the left of the partition, is filled 'withwater I8 which may be circulated through it and through the explosionchamber water jacket l' and a cooling radiator I9 of a conventionaldesign. Circulation may be effected by a pump driven by a motor and theradiator I3 may be cooled by a fan.

The other portion of the second chamber I6, showing the ngure to theright of the partition I6, may be filled with oil 2I which is protectedfrom the heat of the explosions in the explosion chamber l by the cooledwater Il in the rst portion of the second chamber I6.

A stiff, rigid member, such as an aluminum plate 22, is movably mountedin the second chamber I6 at the end remote from the explosion chamber I.Its periphery ilts loosely between the chamber walls so that oilpressures on either side of it are equalized.

Fixed as by a suitable cement to the other side of this plate 22 are theends of a number `of piezoelectric crystal elements 22 whose oppositevends are similarly xed to a massive backing block 24. The block 24 maybe mounted on and supported by a skirt 25, movably engaging with a skirt26 which may be an extension of the outer walls of the chamber Il. Theassembly comprising the backing block 24, the crystals 23 and thealuminum plate 22 and the skirt 2i may be moved bodily toward or awayfrom the explosion chamber I, correct positioning being effected as byturn buckles 21. With this construction the piezoelectric crystalelements are immersed in a protective bath of oil.

The piezoelectric crystal elements 23 may be cut from any suitablemother material, for example, ammonium dihydrogen phosphate (ADP) tovibrate in their fundamental longitudinal vibration mode. 'I'hismaterial and the manner in which it should be cut are described andclaimed in United States Patent to Mason 2,450,010, issued September 28,1948. The crystal lengths may be substantially one-quarter of thewavelength oi a compression wave in the crystal material. Each one isprovided on either side with a conducting plate or nlm 28, 28' whichserves as an electrode in accordance with known principles ofconstruction and operation. Corresponding electrodes 28 may be connectedelectrically in parallel and to one terminal of primary winding 29 of atransformer 30, the other terminal of which may be connected to thecorresponding oppositely located crystal electrodes 28'. For simplicityand convenience of illustration. the electrodes which are specific tolonly a few of said crystal elements are shown so connected to theprimary of transformer 30. it being understood that similar electrodesof the other crystal element may be similarly connected, as indicated.The secondary winding 3I of the transformer 30 may be connected tosupply a desired load 32 and, if direct current is desired, a rectier 33of conventional design may be interposed.

To control the timing of the ignition of the combustible mixture, aportion of the electric energy output from the crystals 23 may be fedback, by way of an adjustable phase controlling device 34, to thespark-gaps II. Similarly, to control the timing of the intake of thecombustible fuel mixture, a portion of the generated energy may be fedback, for example, from the secondary winding 3| of the transformer andby way of another adjustable phase controlling device 35 to actuate thevalve solenoid I0.

Any suitable starting arrangement may be employed, for example, magneto33, energized by a manually operated switch 31 and battery 3l, whichplaces a suitable voltage on the high tension electrodes of thespark-gaps II. This voltage must, of course, be suiliciently high to scause the spark to jump the gaps II.

I'he dimensional arrangements of the invention will be better understoodafter the description of operation of the device which ensues.

The operation of the system is as follows; Assume that a charge ofcombustible vapor or fuel mixture has been drawn into the chamber by wayof the intake valve 2 and that the latter has just closed. A spark isnow caused to take place at the spark-gaps Il which ignites the fuel andsets of! an explosion, causing a high pressure to exist in the head endof the chamber, shown in the ligure as the left-hand end. This conditionof high pressure travels lengthwise of the chamber at a speed equal tothe velocity of sound in the hot gas, which is approximately 1200 feetper second. The condition travels in the form of a substantially planewave because wave travel in other modes is attenuated in the mannerhereinafter described.

The high pressure condition reaches the stiE piston-diaphragm 3 and isthere reflected without alteration of phase and returns toward the headend of the chamber. 'Ihe reflection takes place at the piston surfaceafter the lapse of one-half of the operation cycle. At this instant thepressure at the head end of the chamber has the lowest value it reachesduring a. cycle. Therefore. at or about this instant, the intake valve 2is caused to open once more and a new charge of fuel is driven in by thepump 8 which should provide a pressure in excess of the pressure whichobtains in the explosion chamber at this instant. At the instant thatthe pressure wave reaches the head end of the explosion chamber on itsreturn path after reflection, i. e., after completion of a full cycle ofoperation, the intake valve 2 will have again closed and another sparkis caused to take place at the spark-gaps II. Thereupon the full cycleis repeated.

In order that each explosion shall take place at the instant when thepressure wave due to the prior explosion shall have returned, afterreflection at the piston-diaphragm 3, to the head end oi' the explosionchamber, the chamber should be substantially one-half wavelength long,or a multiple thereof. When this is the case, regions of greatestoscillatory pressure will exist at the two reflecting end faces.Because, at the high frequencies contemplated in this invention,one-half wavelength might result in dimensions which are awkwardlysmall, a number of half wavelengths may be preferable. Thus, with avelocity of propagation of sound of 1200 feet per second and a frequencyof 5000 cycles per second, the full wavelength is about 0.24 feet orabout 7.3 centimeters. With a chamber which is a full wavelength long,operation is the same as above described i'or a half wavelength chamber,except that there will exist a velocity node or high pressure region atthe central plane. 'Ihe exhaust pipe I2, which should be located at apressure node, should in this event be placed one-quarter of the chamberlength from either end, as shown in Fig. l. With a half wavelengthchamber the exhaust may be centrally located.

By proper dimensioning of the quarter-wavelength crystals 23 inaccordance with wellknown principles they may be made resonant at u adesired operating frequency, for example, 5000 cycles per second or amultiple thereof. Precise adjustment of the length of the explosionchamber and so of the wavelength of sound in the gaseous mixture, whichdepends on its temperature, to match the natural frequencyof thecrystals 23 may be effected in any desired manner, for example, byadjustment of the position of the reflecting piston-diaphragm 3 by theturnbuckle I5.

In order to prevent the vibration of the gas column in the explosionchamber at higher modes and restrict its energy so far as possible tothe energy of plane waves, it suices properly to restrict thecross-section of the chamber. Thus, higher modal oscillations will berapidly damped out if the chamber diameter, assuming it to be `ofcircular section, be less than 0.6 times the Wavelength, or in thiscase, 4.3 centimeters. It is advisable to introduce a small factor ofsafety and use a figure of about 0.5, in practice. This sets an upperlimit of 3.6 centimeters to the diameter of the explosion chamber. Foran explosion chamber of rectangular cross-section the correspondingcriterion is that the shorter side of the cross-section should notexceed one-half wavelength. The considerations out of which this designcriterion arises are fully explained in Electromechanical Transducersand Wave Filters by W. P. Mason (Van Nostrand, 1942) at pages 108 to110. i

As stated above, the exhaust pipe I2 should be located at a pressurenodeof the vibrating gas column. This greatly reduces the amount of highfrequency energy lost by way of the exhaust pipe. In order further toreduce such losses, a lter I3 may be interposed in the exhaust pipe,which filter is constructed to offer a high impedance to oscillatoryenergy of the operating frequency while offering only a negligibleimpedance to the steady flow of the exhaust combustion products. Such afilter is known as a lowpass filter. It may be simply constructed of apair of branch pipes, each one-quarter wavelength long, and positionedone-quarter wavelength from the opening of the exhaust pipe I2 into theexplosion chamber I. The theory of operation and construction of suchacoustic lters is well known and is described, for example, in Elementsof Acoustical Engineering" by H. F. Olson (Van Nostrand, 1940). Ifdesired, the circulating Water pipes may likewise be provided withacoustic lters. as indicated. The position of these lters is notcritical. They have the same function as the lters in the exhaust pipeand are subject to the same principles of dimensional design, so as tojustify the use of the same reference numeral I3 for them, as hereindicated. This principle of design would require them to be about fivetimes as long as the filter in the exhaust pipe, hence they are shownbroken at a point intermediate their ends.

The forces due to the repeated reflections of the pressure waves of thegaseous medium on the piston-diaphragm 3 are transferred by the turnbuckle I5 to the piston-diaphragm I4 which, in turn, transfers them intothe liquid medium I8, 2|, which may be one-quarter wave long or an oddmultiple thereof in the second chamber I6. The assembly consisting ofthe two diaphragms 3, I4 and the turn buckle I5 thus acts as a piston,driven by the pressures in the explosion chamber I and driving theliquid medium in the second chamber I6. The latter, in turn, by reasonof its dimensions, acts as a quarter-wave acoustic transformer totransfer the pressure energy of the exmatch such widely diIIerentimpedances presents considerable difilculties. This is especially truewhen it is desired to restrict the vibratory energy to the form of planewaves and avoid production of wasteful higher modal oscillations,because, as explained above in connection with the dimensions of theexplosion chamber, this consideration likewise sets an upper limit ofone-half wavelength to the diameter (or shortest side) of thecross-section of the second chamber. In water or oil the speed ofpropagation of sound is about four times its value in the hot gases ofthe explosion chamber, i. e., about 4800 feet per second, and thewavelength at a frequency of 5,000 per cycle is about 28 centimeters.Consequently, the shortest side of the cross-section of the secondchamber should not exceed 14 centimeters. A

factor of safety is advisable so this dimension has been taken assomewhat less than I4 centimeters, e. g., 12 centimeters. Without thisrestriction it would be possible to match the low impedance of the gascolumn to the high impedance of the crystals by mere adjustment of therelative crosssections' of the ilrst and second chambers. The theory,construction and mode of operation of acoustic impedance transformerswhich function byreason of a change in cross-section is welld0 known inthe art and is explained for example, in

Electromechanical Transducers and Wave Filters, by W. P. Mason (VanNostrand, 1942)'. However, in order to avoid higher modal oscillations,this cross-section area ratio cannot b`e increased without limit. In theparticular case selected assan example, and assuming circularcross-sections both for the explosion chamber and the transformerchamber, this cross-section area ratio ls therefore limited to thefigure rial of the operating transformer medium. The

mechanical impedance looking into the end of quarter wavelength crystalshas been determined to be about 0.2 of the characteristic impedance ofthe crystal material for an A P crystal. Taking the area of the crystalside of the plate 22 which is filled with crystal ends to be one-halfthe total plate area, the total impedance worked into is therefore600,000X0.2X0.5 or 60,000 mechanical ohms per square centimeter of platearea or a total of asaassc 7 'I'he impedance at the piston diaphragmlooking into the explosion chamber is 50x 42=62s mechanical ohms Byreason of the cross-section change associated with the diameter changefrom 4 centimeters to 12 centimeters alone, the characteristic impedancelooking into the liquid medium can be made =9 times as great as theimpedance (50 mechanical ohms per square centimeter) of the gaseousmedium or 450 mechanical ohms per square centimeter, while the totalimpedance looking into this medium from the the same point can be madel2 4 71- =81 times as great square centimeter will be equal to \/45060,0l or 5200 mechanical ohms per square centimeter.

This impedance is too high for a gas and too low for a liquid. Inaccordance with the invention, however, it is realized by a combinationof a liquid and a gas. The characteristic impedance of water or oil isabout 150,000 mechanical ohms per square centimeter and that of air orgas is about 50 mechanical ohms per square centimter. I'he desiredimpedance, 5200 mechanical ohms per square centimeter, is about 1/so ofthe greater of these figures and about 100 times the lesser. It has beenfound that a proper admixture of two materials of diderentcharacteristic impedances partakes of the nature of both components. Inparticular, if one part by volume of finely divided air bubbles isintermixed with 99 parts by volume of water, the impedance of themixture will be close to the desired value of 5200 ohms per squarecentimeter. However, it is impossible to hold the proper amount of airin the form of minute bubbles in suspension in the liquid. Therefore, inaccordance with the invention, the proper amount of air by volume isretained in position in the form of minute air bubbles contained in asuitable cellular retainer such as a sheet of sponge rubber I 1. Boththe material and the volume of the rubber have a negligible effect onthe operation, the rubber serving for all practical purposes merely as amatrix in which the air bubbles are embedded.

The air and the sponge rubber in which it is contained are much morecompressible than the liquid on either side of it. Therefore, thisconstruction greatly reduces the length of the transformer chamber I8for a given wavelength. For example, were the transformer chamber whollyfilled with water or oil, and one-quarter wavelength long from thepiston Il to the crystal-supporting plate 22 it would measure 7.5centimeters at an operating frequency of 5,000 cycles per seccond. Withthe interposition of the sponge rubber air-supporting sheet l1, however,its length, for the same behavior, is reduced to 1.5 centime- 8 ters.the sponge rubber sheet being only about 0.25 centimeter in thickness.This reduction in length may be of considerable advantage at lowerfrequencies where the length of a quarter wave might be awkwardly large.In the present example, however, the length of 7.5 centimeters is notawkwardly large. On the contrary, the length of 1.5 centimeters mayunder some conditions be awkwardly small. If such should be the case,the transformer chamber may be made an odd multiple oi' a quarter wavein length. for example, three-quarters of a wavelength, in which casethe dimension of 1.5 centimeters becomes 4.5 centimeters. The spongerubber diaphragm II should then preferably be placed at a distance ofapproximately one-third the length of the transformer chamber measuredfrom the plate 22; i. e., at the pressure node which exists onequarterwavelength from the high pressure end of the chamber I6. Thisarrangement has been selected for illustration in the ligure. Preciseadjustment of the transformer chamber I0 to an odd number of quarterwavelengths is accomplished by movement of the assembly consisting ofthe crystals 2l, the plate 22 and the backing plate 24 toward or awayfrom the explosion chamber I. This is effected by rotation of the turnbuckles 21. Inward movement requires removal of some of the oil andwater from the chamber I0 and outward movement requires addition ofwater and oil. Stop cocks Il, 4I may be provided for this purpose.

The composite impedance transformer of the invention thus permitsmatching of impedances over a wider range than would be possible at thehigh frequencies contemplated and without the excitation of higher modaloscillations and consequent energy losses, by adjustment of thecross-section ratio alone.

The quantitative relations employed in the foregoing example may begeneralized, for a plurality of uuid media as follows:

Let

pi=pressure In the explosion chammcle mi br (ahead or the c ange incross- -mammfwww pz=pressure In the transformer iangiggle velocitychamber Il (follow- I ing the change in Zh'imyse cross-section)Zs=impedance of plate 22 and crystals 2l Z=characteristic impedance offirst component fluid Zs=characteristic impedance of second componentfluid Za=characteristic impedance of third component iltlid e etc.Zo=characteristic impedance of composite fluid medium Then, ahead of thechange in cross-section Zei-' (1) and following the change,

Zi=gj 2) But since volume velocities and pressures are continuous acrossthe cross-section change,

p1=in (s) nA1=iiAi 4) Dividing (a) by (4) and substituting 1) and i2).Zs Ai A: l

zfz. 5)

If there be no change in cross-section. ('I) reduces to the morefamiliar expression for a quarter wave transmission line.

To obtain a medium having this characteristic impedance Zo by combiningdifferent fluid media of characteristic impedances Z., Zi, Ze, etc., andoccupying volumes V., Vb, Cc, etc.. it is only necessary to adjust theproportions in accordance with the formula With only two componentmedia, formula (9) reduces to It will be found by substitution that thefigures of the example given above satisfy this formula.

The impedance transformer has been described in connection with its usein applicants power source, wherein the explosion chamber (source)impedance is low and the crystal (receiver) impedance is high. It isequally applicable to the inverse transformation from a high sourceimpedance to a low receiver impedance.

It is recommended that the apparatus be operated at a fairly high energylevel. For example, if the oscillating pressure within the explosionchamber I has an amplitude of one atmosphere, the total pressure thenvaries between =(V.+Vi)Zo (10) nero and two atmospheres. When this highvalue oi' alternating pressure is maintained the energy density will rbegiven by the formula:

Energy density- P--:LX 10"- 1000 watts per square centimeter wherePm=peak value of alternating pressure (one atmosphere) p=density ofgaseous medium v=velocity of sound in the gaseous medium Not all of thisenergy is transmitted to the transformer chamber I8, since if it were sotransmitted, standing pressure waves could not be maintained in theexplosion chamber I. However, when one-quarter of the stored energy istransferred in each operating cycle, one-quarter of the above factor or250 watts per square centimeter becomes available for transfer. With anexplosion chamber of the dimensions shown and discussed above, thisenergy density results in' a transfer oi about three kilowatts. Sincethe overall length of the entire system is not more than about two feetand its overall diameter not more than about six inches, an exceedinglycompact unit. capable of delivering close to three klowatts of electricpower, is thus made availa le.

Operation at high energy levels oiers the further advantage that thefuel pump il,l which injects the atomized fuel at the low pressureinstants of the combustion cycle, need work only against very lowpressures and therefore need require only a small amount of power.

What is claimed is:

l. A source of oscillatory energy which comprises a substantially closedacoustic resonant chamber, thermal means for setting up standingpressure waves of a gas within said chamber at an orderly high frequencyand a pressureresponsive piezoelectric element coupled to said chamberin such fashion as to be actuated by the pressures of said waves.

2. A source of oscillatory energy which comprises a pressure-supportingvessel, an elastic fluid within said vessel, an elastic member coupledto said fluid, thermal means for producing pressure changes of saidfluid in ordered time sequence, and means for deriving oscillatoryelectric energy from strains in said elastic member.

3. A source of oscillatory energy which comprises a pressure-supportingvessel, an elastic means for producing pressure changes of said fluid inordered time sequence, and means for deriving oscillatory electricenergy from strains in said elastic member.

5. A source of oscillatory energy which comprises a closed vessel, awave-supporting fluid within said vessel, a mechanical-electricaltransducer coupled to said fluid, said transducer beassassin l in'gadapted w deliver electric energy in response to mechanical pressuresthereon, and means for developing standing waves of compression in saidfluid of a wavelength such that said transducer is coupled to a highpressure region of said fluid.

6. A source of oscillatory energy which comprises a closed vessel, afluid within said vessel capable of supporting standing waves of anatural frequency and wavelength determined by the nature of the fluidand the dimensions of the vessel. means for developing standing waves insaid fluid. and a mechanical-electrical transducer element coupled tosaid fluid, said element having a natural oscillation frequencysubstantially like the natural frequency of said standing waves.

7. A source of oscillatory energy which comprises a closed vessel, afluid within said vessel capable of supporting standing waves of anatural frequency and wavelength determined by the nature of the fluidand the dimensions of the vessel, means for developing standing waves insaid fluid, a mechanical-electrical transducer element coupled to saidfluid, said element having a natural oscillation frequency substantiallylike the natural frequency of said standing waves, a load circuit, andelectric connections from said transducer element to said load circuit.

8. A source of oscillatory energy which comprises a closed vessel, afluid within said vessel capable of supporting standing waves of anatural frequency and wavelength determined by the nature of the fluidand the dimensions of the vessel, means for developing standing waves insaid iluid, a mechanical-electrical transducer element coupled to saidduid, said element having a natural oscillation frequency substantiallylike the natural frequency of said standing waves. a load circuit, meansfor supplying electric energy derived from said transducer element tosaid load circuit, and means for feeding back a portion of said electricenergy to maintain said standing waves.

9. A source of oscillatory energy which comprises a pressure-supportingvessel, a fluid within said vessel capable of supporting standing wavesof a natural frequency and wavelength determined by the nature of thefluid and the dimensions of the vessel, means for developing standingwaves in said fluid, said vessel having a. length substantially equal toan integral number of half wavelengths of sound in said uid and having across-section whose shortest dimension is less than said halfwavelength, a movable piston for adjusting the length of said vessel andfor responding to the changing pressures in said vessel, a vibratorymechanical-electrical transducer whose natural frequency accords withthe frequency of said standing waves and impedance transformer means fortransferring the energy of pressures exerted upon said piston to saidmechanical-electrical transducer.

l0. A source of oscillatory energy which comprises a pressure-supportingvessel, a iluid within said vessel capable of supporting standing wavesof a natural frequency and wavelength determined by the nature of thefluid and the dimensions of the vessel, means for developing standingwaves in said fluid, said vessel having a length substantially equal toan integral number of half wavelengths of sound in said iluid, andhaving 'a cross-section whose shortest dimension is less than said halfwavelength, a movable piston for adjusting the length of said vessel andfor responding to the changes in pressure in laid vessel, a vibratorymechanical-electrical transducer whose natural frequency accords withthe frequency of said standing waves, impedance transformer means fortransferring the energy of pressures exerted upon said piston to saidmechanical-electrical transducer. and means for feeding back electricalenergy developed by said transducer to control the operation of saidstanding wave developing means whereby to control the frequency of saidwaves.

11. A source of oscillatory energy which comprises a pressure-supportingvessel, a fluid within said vessel capable of supporting standing wavesof a natural frequency and wavelength determined by the nature of thefluid and the dimensions of the vessel, means for developing standingwaves in said fluid, said vessel having a length substantially equal toan integral number of half wavelengths of sound in said fluid and havinga cross-section whose shortest dimension is less than said halfwavelength, a movable piston for adjusting the length of said vessel andfor responding to the changes in pressure in said vessel, a vibratorymechanical-electric transducer whose natural frequency accords with thefrequency of said standing waves, impedance transformer means fortransferring the energy of pressures exerted upon said piston to saidmechanical-electrical transducer, an exhaust pipe connecting with saidvessel, and an acoustic lter connected to said exhaust pipe, adapted toblock high frequency pressure energy while permitting release ofpressures not directly associated with said standing waves.

l2. A source of oscillatory energy which comprises a pressure-supportingvessel, an elastic fluid within said vessel, means for setting upstanding pressure waves of said fluid within said vessel, amechanical-electrical transducer element of high input impedance, andmeans for transforming the standing wave pressure energy of said chamberto match said high input impedance which comprises a second chambercontaining a liquid and a layer of trapped bubbles of gas.

13. A source of oscillatory energy which comprises a pressure-supportingvessel, a gaseous medium of low impedance within said vessel, means forsetting up standing pressure waves of 'said medium within said vessel. amechanicalelectrical transducer element of high input impedance, andmeans for transforming the standing wave pressure energy of said chamberto match said high input impedance which comprises a second chambercontaining a liquid and a layer of a material comprising a multitude ofseparate cells, each cell containing a gas.

14. A source of oscillatory energy which comprises a pressure-supportingvessel, an elastic fluid within said vessel, means for setting upstanding pressure waves of said fluid within said vessel, amechanical-electrical transducer element of high input impedance, andmeans for transforming the standing wave pressure energy of said chamberto match said hlgh input impedance which comprises a layer of a soft.solid material comprising a. multitude of separate cells, each cellcontaining a gas.

15. In a system for developing electrical energy from mechanical energy,and in combination with a low characteristic impedance source ofoscillatory pressures and a high impedance mechanical-electricaltransducer adapted to deliver oscillatory electric current when actuatedby 13 oscillatory pressures, an impedance-matching transformer whichcomprises a chamber coupled to said source and to said transducer, aliquid mass in said chamber, and a plurality of minute gas bubblessuspended in said liquid.

16. In a system for developing electrical energy from mechanical energy,and in combination with a low characteristic impedance source ofoscillatory pressures and a high impedance mechanical-electricaltransducer adapted to deliver oscillatory electric current when actuatedby oscillatory pressures, an impedance-matching transformer whichcomprises a chamber coupled to said source and to said transducer, aliquid mass in said chamber, and a sheet of soft, liquid-tight cellularmaterial suspended in said liquid, the cells of said material containinggas.

17. A confined column of gas, a mechanicalelectrical transducer, aliquid acting as a coupling medium between said gas column and said zo14 to maintain said standing waves, said transducer, coupling medium,and gas column being tuned to the same natural frequency of vibration.

WARREN P. MASQN.

REFERENCES CITED The following references lare of record in the ille ofthis patent:

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